In solid-state imaging devices such as video camcorders, digital still cameras and camera-equipped cell phones, CCDs and CMOS image sensors which are solid-state image capture elements for color images are used. These solid-state image capture elements, in their light-receiving sections, utilize silicon photodiodes that are sensitive to near-infrared ray imperceptible to human eyes. In such solid-state image capture elements, it is required that spectral luminous efficacy correction be performed so that colors natural to human eyes are produced; therefore, an optical filter which selectively transmits or cuts light rays in a specific wavelength range is often used.
As such optical filters, those filters produced by a variety of methods have been conventionally used. For example, optical filters such as near-infrared cut filters in which a transparent resin is used as a base material and a near infrared-absorbing dye is incorporated in the transparent resin are widely known (see, for example, Patent Document 1). However, the optical filter described in Patent Document 1 does not necessarily have sufficient near infrared-absorbing capacity.
Further, the present applicant has proposed an optical filter comprising a squarylium-based compound having a specific structure (see Patent Document 2). When such an optical filter is used, the incidence angle dependence of the optical properties in the near-infrared region can be reduced, so that the viewing angle can be better improved than existing optical filters.
However, the use of only a compound showing absorption in the near-infrared region may not be able to sufficiently improve the incidence angle dependence of the optical properties in the near-infrared region such as a wavelength range of 300 to 420 nm. For example, as shown in FIG. 1, when a near-ultraviolet light B reflected by the surfaces of optical filter 6 and lens 5 enters the optical filter 6 at an angle larger than 0°, the reflected light cannot be cut sufficiently, so that violet and blue obscure images may be generated, which leads to a reduction in the camera image quality.